1. Field of the Invention
This invention relates to a polymeric composition comprising a thermoplastic or thermoset polymer, elemental red phosphorus, and an aldehyde or .beta.-carbonyl-containing ketone, or mixtures thereof.
2. Description of the Prior Art
Elemental phosphorus, particularly red phosphorus, has been described as an additive in a number of polymeric systems. The amorphous elemental red phosphorus, either alone or in combination with other additives, has been described as an effective flame retardant additive in polymeric systems. Red phosphorus has been added to, for example, polyurethanes, polyamides, polyformaldehydes, polyepoxides, polyethylene terephthalate, epoxy resins, styrene/acrylonitrile copolymers, rubber blends, polyvinyl chloride, polyoxymethylenes, polycarbonates, blends of polyphenylene ether and styrene resins, and olefin polymers as well as various thermoset polymers.
However, on exposure to air at normal temperatures and humidities, red phosphorus reacts with the water vapor and oxygen to form phosphine. Also, during the storage and handling of red phosphorus and additionally, at the elevated temperatures used in processing thermoplastics and curing thermosetting materials, phosphine is formed. Phosphine is a highly toxic gas. Thus it is highly desirable to eliminate formation of phosphine when using the phosphorus. This can be accomplished by the inclusion of a substance which binds the phosphine.
U.S. Pat. No. 3,883,475 describes various inorganic salts such as HgO, PbO.sub.2, CuO, HgCl.sub.2 and AgNO.sub.3 used to form addition compounds with phosphine in order to bind the phosphine formed from red phosphorus. However, these salts are toxic environmental pollutants and/or expensive and, hence, their general utility is questionable.
British Pat. No. 1,437,301 describes amidosulfonic acid and ammonium bisulfate as effective in reducing phosphine production in phosphorus containing polyolefin compositions. However, the high water solubility of these additives can lead to reduced effectiveness in certain environments.
U.S. Pat. No. 3,808,127 describes the impregnation of red phosphorus with trioxane and its use for the production of flame resistant thermoplastic compositions. The red phosphorus is impregnated with the trioxane to reduce dust, which red phosphorus produces due to the large amounts of fines present in the red phosphorus. Also, red phosphorus can readily ignite when in contact with hot surfaces, such as are found in processing machines. Such ignition constitutes a considerable fire risk. The impregnation of red phosphorus with trioxane is stated to reduce the risk of ignition. However, column 1, lines 57 to 62, of U.S. Pat. No. 3,808,127 states: "It is a special advantage of red phosphorus which has been impregnated in accordance with the invention that the impregnated trioxane, owning to its low boiling point (116.degree. C.), can be rapidly and completely removed from the thermoplastics melt after the impregnated red phosphorus has been incorporated. The phosphorus is thus uniformly distributed in the thermoplastics melt. Moreover, the phosphorus filled thermoplastic is obtained free from the impregnant which could change its properties". Thus, the patent suggests that the trioxane is not present when the red phosphorus is exposed to conditions which could result in the formation of phosphine.
Thus, there exists a need to eliminate the formation of phosphine during the storage and handling of compositions containing elemental red phosphorus and also during the processing (thermoplastics) and curing (thermosets) of these compositions at elevated temperatures.